1. Field of the Invention
The present invention relates to an optical scanning apparatus for carrying out optical writing on a photosensitive drum or the like with use of a laser beam and a support member for an optical scanning apparatus in an image forming apparatus such as a laser beam printer (hereinafter referred to as “LBP”), a digital copying machine, and a digital facsimile machine.
2. Description of the Related Art
Image forming apparatus such as an LBP is configured to form an image on a recording material by forming an electrostatic latent image on a photosensitive drum in accordance with a desired image, developing the electrostatic latent image into a toner image, and by transferring the toner image onto the recording material. To form a desired electrostatic latent image on the photosensitive drum, there is used an optical scanning apparatus for irradiating and scanning the photosensitive drum with a laser beam.
Therefore, the print accuracy of such an image forming apparatus is significantly affected by the mechanical accuracy of the optical scanning apparatus. In particular, in an optical deflector for rotationally driving a rotating polygon mirror, the rotation center of the rotating polygon mirror, which serves as a reference of an optical system of the LBP, needs to be positioned with respect to an optical reference position of an optical box with high accuracy.
In view of the above, there is generally employed such positioning structure that a shaft or bearing of the optical deflector is fitted into a fitting hole provided at the optical reference of the optical box.
Conventionally, an optical deflector including a polygon mirror and a motor unit for rotating the polygon mirror is generally fixed with screws at three points surrounding the motor. In this case, a board is fixed in conformity to bearing surfaces at the respective screw fixing portions. Therefore, when the bearing surfaces are inclined, the board is distorted and the shaft of the motor unit of the optical deflector is inclined.
Further, the inclination of the rotation shaft of the optical deflector, which is called shaft inclination, may cause distortion of a spot-shape of the laser beam on the photosensitive drum, resulting in deterioration in image quality.
According to Japanese Patent Application Laid-Open No. 2005-201941, the optical deflector is fixed to the optical box with use of a screw and a spring, and the screw is tightened and loosened after the optical deflector is fixed, to thereby adjust the push-in amount and control the shaft inclination.
In the structure disclosed in Japanese Patent Application Laid-Open No. 2005-201941, however, the assembly process becomes complicated for the sake of shaft inclination control, thus leading to a problem in that the number of steps is increased.